Two F-35A and two F-35B aircraft fly over Edwards Air Force Base, Calif., in June 2013. (Lockheed Martin)

The F-35 Joint Strike Fighter is often touted as the most advanced fighter in the world, whose complex systems are held together by millions of lines of code. So when the Pentagon’s top weapons tester declares the current software “unacceptable,” it tends to make waves in the defense world.

That’s what happened this week, as the Department’s Office of Test and Evaluation (OT&E) released its annual report on the status of the F-35 with a strong rebuke of the progress F-35 supporters touted in 2013, including a warning that software development has lagged so far behind that it may cause the Marines to miss their initial operating capability (IOC) date in 2015.

“The program plans to complete Block 2B fight testing in October 2014; however, there is no margin for additional growth to meet that date,” the report found. “Projections for completing Block 2B fight testing using the historical rate of continued growth ... show that Block 2B developmental testing will complete about 13 months later, in November 2015, and delay the associated feet release to July of 2016.”

The Marines intend to go to IOC with the Block 2B software; the Air Force is scheduled to follow with its F-35A in December 2016 with Block 3I, which is essentially the same software on more powerful hardware. The Navy intends to go operational with the F-35C in February 2019, on the Block 3F software.

Additionally, the testers warn that the F-35’s Autonomic Logistics Information System (ALIS) is “immature and behind schedule.” Any further delays to the software development, which is at the core of operations, maintenance and supply-chain management for the platform, could prove problematic for the program going forward.

Despite hopes from outside groups who view the F-35 as a legendary waste of taxpayer funds, the Pentagon seems unlikely to move away from the plane, regardless of how poorly it comes out in testing reviews like the one put forth this week.

Because the F-35 is so close to IOC and escaping a dreaded “death spiral” of partner nations dropping from the program, hence raising the cost per plane to an unaffordable level, proponents would also argue against any slow-down on the rate of production.

“I am fighting to the end, to the death, to keep the F-35 program on track,” said Gen. Michael Hostage, head of the Air Force’s Air Combat Command. “For me, that means not a single airplane cut from the program, because every time our allies and our partners see the United States Air Force back away, they all get weak in the knees. This program will fall apart if the perception is that the Air Force is not committed to this program.

“I am fighting to the end, I am going to fight to the death to protect the F-35 because I truly believe that the only way we will make it through the next decade is with a sufficient fleet of F-35’s.”

Other problems were identified as well in the report, including the conclusion that the plane’s electrical system is vulnerable to ballistic fire “remains an open question.” A number of cracks were also found during tests conducted in 2013. Cracks led to the February 2013 stand down of the entire F-35 fleet. In March, the discovery of excessive wear on the jet’s rudder hinge attachments grounded the test fleet at Edwards Air Force Base, Calif. Cracks were also found on a test-model put under stress as part of durability testing in late September.

The F-35 review is part of a larger report, due Wednesday morning, looking at DoD’s largest acquisition programs.

The OT&E report often conjures mixed emotions in the defense world. While reformers and advocates hold it up as a paragon of oversight on billion-dollar programs, others argue that it focuses too much on process and not enough on results.

Lockheed Martin chose to look on the bright side of the report, citing “a tremendous amount of positive information in the 2014 DOT&E report about the F-35 program’s progress” in a company statement, including the number of weapons tests completed and the fact that 7.4 million of the 8.4 million lines of code for the plane have been flight tested already.

“Lockheed Martin is confident we will complete flight testing of the software required for Marine Corps Initial Operational Capability this year,” the company statement read. “The Marines plan to declare IOC between July and December of 2015. We plan to release the required combat ready software to the F-35 production fleet no later than July 2015.”

That confidence was echoed by the Pentagon office in charge of the F-35 program.

“There were no surprises in the report; all of the issues mentioned are well-known to us, the F-35 international partners and our industry team,” Joe DellaVedova, F-35 Joint Program Office spokesman, wrote in a Pentagon statement. “Although the report is factually accurate, it does not fully highlight the F-35 enterprise’s efforts to address and resolve the known technical and program related challenges.”

“We are confident about delivering the F-35’s initial warfighting capability to the U.S. Marine Corps in July 2015,” the statement continued. “To address reliability and maintainability issues, the JPO has established a reliability improvement program. In addition, we stood up an air system readiness cell with a focus on tackling top degraders to improve overall F-35 readiness.”